OBJECTIVES: To examine the evolution of the rate of admissions for ambulatory care sensitive conditions in beneficiaries of a health care plan, monitoring of access to the health system and its performance and identifying strategies that will enable the improvement of the health situation of the population and the appropriate allocation of resources. METHODS: Retrospective analysis of 212,360 hospital admissions, occurring between 1999 and 2008, among beneficiaries of a health care plan, resident in Brazil. The outcome of the study was the proportion of admissions for primary care sensitive conditions, identified by ICD-10. The proportion of these admissions in relation to the total hospital admissions was established, as well as the quotient for the number of hospital admissions and the population, either total or by age group and specific causes, besides hospital direct costs. The significance was tested and estimates of the rates were defined based on their 95% confidence intervals. RESULTS: Admissions for primary care sensitive conditions accounted for 55,307 of 212,360 admissions reimbursed by the health plan (26.0%). The rate of admission for primary care sensitive conditions fell by 28.0% during the period (from 347.6 to 250.3 per 10 thousand). The most frequent cause was gastroenteritis (30.9%), followed by arterial hypertension (13.6%), cerebrovascular diseases (9.6%), heart failure (8.1%), kidney and urinary tract infections (6.8%), diabetes mellitus (5.8%) and angina pectoris (5.5%). The mean annual expenditure on admissions was R$15,232,494 against R$51,440,680 for other conditions (22.8%). CONCLUSIONS: The reduction observed in the rate of admissions for primary care sensitive conditions suggests possible improvements in primary health care. Further actions and strategies could reduce the number of avoidable admissions and contribute to the financial balance of the health care plan.